1. Field of the Invention
The present invention relates to intake valve devices for controlling the flow rate of intake air that may be supplied to an engine, such as an internal combustion engine.
2. Description of the Related Art
A known intake valve device is shown in FIG. 8 and generally comprises a throttle body 101, a throttle shaft 106, and a throttle valve 130. A substantially cylindrical bore 103 is formed within the throttle body 101 so that intake air flows through the bore 103. The throttle shaft 106 is rotatably mounted in the throttle body 101 and extends across the bore 103. A slit 107 is formed so as to extend through the throttle shaft 106 in a diametrical direction. The slit 107 is elongated in an axial direction of the throttle shaft 106. The throttle valve 130 has a substantially circular configuration. The throttle valve 130 is inserted into the slit 107 of the throttle shaft 106 and is secured thereto via screws 114. As the throttle shaft 107 rotates, the throttle valve 130 rotates within the bore 103, so that the bore 103 is opened or closed by the throttle valve 130. This type of intake valve device is disclosed in Japanese Laid-Open Patent publication No. 11-101137.
In general, in order to form the slit 107 within the throttle shaft 106, a rotary tool such as a disk-shaped rotary cutter 140 (shown in FIG. 10) is rotatably driven. The rotary cutter 140 is moved toward and away from the throttle shaft 106 in the diametrical direction of the throttle shaft 106 (perpendicular to the central axis of the throttle shaft 106) as indicated by arrows Y1 in FIG. 10. The rotary cutter 140 has a diameter larger than a diameter of the throttle valve 130 (indicated by the two-dashed line in FIG. 10). Thus, the rotary cutter 140 is moved toward the throttle shaft 106 (downward as viewed in FIG. 10) in order to cut the throttle shaft 106, forming the slit 107 so as to have a predetermined width (length in right and left directions as viewed in FIG. 10). After which, the rotary cutter 140 is moved away from the throttle shaft 106 (upward direction as viewed in FIG. 10). This method results in two inclined, or tapered in the downward direction, end walls 107a of the slit 107, spaced apart from each other in the longitudinal direction (in the axial direction of the throttle shaft 107). In addition, a tolerance may be given to the slit 107 in order to take into account the possible variations in the size of the disk 130 or the slit 107 due to differences in machining operations. The tolerance may increase the distance between the end walls 107a. 
Therefore, according to the design of the publication, it is inevitable that channels “A”, i.e., clearances, as shown in FIG. 9 are more or less formed between the circumferential edge surface of the disk 130 and the end walls 107a of the slit 107. When the throttle valve 130 is in a fully closed position, the channels “A” may serve as intake air bypass channels causing leakage of the intake air, as indicated by an arrow Y in FIG. 9. The flow rate of possible leaking intake air may be increased over a situation where either no channels “A” or smaller channels “A” exist. The leaking intake air may not present a problem when the throttle valve 130 is in the open position, because the intake air may flow more readily through the open bore 103.